Process of making laminated glass



Patented Aug. 15, 1933 1,922,893 raocass or mxnvcmmma'rcn GLASS PATENT OFFICE J amesW. Kamerer and Earl L. Fix, New Kensington, Pa., assignors to Duplate Corporation, a Corporation of Delaware No Drawing.

Application January 16, 1932 Serial No. 587,152

3 Claims.

Theinvention relates to a process of making the so called laminated or safety glass which ordinarily consists of two sheets of glass cemented to the opposite sides of cellulose nitrate plastic, 5 such as celluloid, which contains about 70% nitro-cellulose and 28% camphor. The present invention relates to the step of cementing the sheets together when a water soluble cement, such as gelatin, casein, gliadin or sericin, is used. Such cements are the most satisfactory of any so far discovered, but the results attained have not been uniformly good, as indicated by exhaustive tests along two lines; namely, break tests, and roof exposure tests. The roof test involves an exposure of the sample to weather conditions over a long period of time, and the break test involves breaking the sample with a metal ball under certain conditions asto weight and drop, which havebeen'more or less standardized. The roof exposure tests develop a certain amount of edge separation with some samples, while in other cases the break. tests show poor adhesion. The object of the present invention is to overcome these difficulties and produce a laminated glass which is uniformly free from edge separation and which uniformly shows good adhesion as evidenced by the break tests:

We have found that this result can be secured by properly conditioning the celluloid. Such conditioning involves the regulation and distribution of moisture through the plastic sheet pre? liminary to the laminating operation. If .the moisture content ranges above a certain percentage which we have determined, edge separation is liableto occur in the finished product, although the break tests of such product'are entirely satisfactory. 0n the other hand, if the moisture content runs below a certain percentage, which we have also determined, the break trouble is experienced with edge separation. Further, the moisture must be well distributed through the body of the plastic sheet, so that 5 tests show unsatisfactory adhesion, although no.

. 28 per cent'of camphor.

from 1.2 to 1.8 per cent, the relative humidity of plus or minus five is maintained. A convenient temperature is 70 F. plus or minus five. f 'It will be understood that under humidity conditions as they exist in the North Atlantic States, remote from the sea board, a considerable part, of the plastic sheets will normally have a moisture content lying between the limits specified, but that such content may depart considerably from these limits, in some cases, as low as 1% and in others as high as 2.5%, and that the conditioning is necessary only to insure a proper moisture content during those periods. when the atmosphere is either too moist or too dry to hold the percentage of moisture between the desired limits as heretofore pointed out. At times the plastic sheets are too low in moisture under existing atmospheric conditions, but in the location given the plastic will very often, particularly in summer, have too high a moisture content, so that the conditioning step involves a drying out of the plastic to bring it to the desired condition as to moisture content. Further, conditions of storing the celluloid in packs may result in an uneven distribution of moisture throughthe sheets, the moisture content at the edges, difiering very substantially from that at the center of the sheets. The longconditioning period equalizes this moisture content so that each increment of the sheet area is conditioned the same with a consequent uniformity of adhesion throughout the cemented area.

The moisture contents heretofore referred to and asset forth in the claims are not, as a matter of fact, absolute contents, but are figured on the assumption that the plastic is bone dry after drying over calcium" chloride as a dehydrater. The term cellulose nitrate plastic, as used heretofore and in the claims, refers to the standard type of material comprising approximately 70 per cent of nitro-cellulose and The limits for moisture content, as herein recited, may or may not be advantageous with types of celluloid compositions involving departures from the composition above stated.

We'claim: I

1. A process of making laminated glass, which consists in treating a sheet of cellulose nitrate plastic in an atmosphere controlled as to moisture content for a period of time such as to secure a. uniform distribution therethrough of 1.2% to 1.8% of moisture, and then employing a Water soluble adhesive to secure glass sheets to the opposite side of the sheet of plastic.

2. A process of making laminated glass, which consists in treating a sheet of cellulose nitrate plastic in an atmosphere controlled as to moisture content for a periodof time such as to secure a uniform distribution therethrough of 1.2% to 1.8% of moisture, and then securing sheets of glass to the opposite sides of the plastic sheet'by the use of gelatin cement. 

